This can be related to the influence of clay on carbonate particles that appeared in clay size
, could not act as clay particles specific particle surface and hence the water content.
Weathering sequence of clay size
minerals in soils and sediments.
Different mechanisms have been suggested to account for this textural control of SOC retention, including higher sorption area as clay content increases, resulting in larger SOC pools in the clay size
(Zinn et al.
In these soils, mineralogy of the clay size fraction is dominated by either kaolinite and/or crystalline and amorphous iron and aluminum oxy-hydroxides, minerals with high pH at the point of zero charge (PZC) (SPOSITO, 1989) due to surface functional groups such as ferrol (FeO[H.
2005; DI; CAMERON, 2002) due to an excess of negative charge on the colloidal particles associated with, either, higher SOM content, neutral pH and predominance of smectites and vermiculites in the clay size fraction (with permanent negative surface charge).
Furthermore, according to torsional ring shear tests by Stark and Eid  the value of [phi]' may decrease by 4' as the clay size
fraction increases from less than 20% to more than 50% or as effective normal stress increases from less than 50 kPa to more than 400 kPa.
This investigation was conducted on the whole soil and sand, silt, and clay size fractions of surface (0-10 cm) horizons of 7 soils (Table 1).
Note that KELL 9 contains mica in the sand, silt, and clay size fractions and KTG 7 contains no mica and only a little inhibited vermiculite in its clay fraction (Figs 1, 2).
The rate of loss of organic C from the clay size
fraction is generally lower than that from the other fractions and the whole soil (Table 5) (Dalal and Mayer 1986b, 1986c, 1986d; Parton et al.
4b, c) show basically the same particle size composition, with low contents of sand, and 2 prominent modes in coarse silt and clay sizes
This can be achieved by pressing down with the thumb, measured clay sizes
on to the floor or back of the hump mould until a complete hemisphere is formed.